Wnt/��-catenin signaling in hepatic organogenesis

Wnt/β-catenin signaling has come to the forefront of liver biology in recent years. This pathway regulates key pathophysiological events inherent to the liver including development, regeneration and cancer, by dictating several biological processes such as proliferation, apoptosis, differentiation, adhesion, zonation and metabolism in various cells of the liver. This review will examine the studies that have uncovered the relevant roles of Wnt/β-catenin signaling during the process of liver development. We will discuss the potential roles of Wnt/β-catenin signaling during the phases of development, including competence, hepatic induction, expansion and morphogenesis. In addition, we will discuss the role of negative and positive regulation of this pathway and how the temporal expression of Wnt/β-catenin can direct key processes during hepatic development. We will also identify some of the major deficits in the current understanding of the role of Wnt/β-catenin signaling in liver development in order to provide a perspective for future studies. Thus, this review will provide a contextual overview of the role of Wnt/β-catenin signaling during hepatic organogenesis.Key words: liver development, liver cancer, liver regeneration, Wnt signaling, proliferation, differentiationThe Wnt/β-catenin pathway is an evolutionarily well-conserved pathway that has proven to be essential to normal cellular processes such as development, growth, survival, regeneration and self-renewal.^1–5 Its diverse functions also include the initiation and progression of cancer.⁶ In fact, one area in which this pathway has been extensively studied is in liver cancer.Mutations of Wnt/β-catenin pathway members in hepatocarcinogenesis are common. For example, 90–100% of hepatoblastomas contain mutations in adenomatous polyposis coli (APC), CTNNB1 and/or Axin1/2, which causes cytoplasmic and nuclear localization of β-catenin.^7–9 Axin1 and β-catenin mutations have also been identified in approximately 25% of hepatocellular carcinomas,^10–12 while overexpression of the frizzled-7 receptor¹³ and glycogen synthase kinase-3 (GSK-3) inactivation¹⁴ can also lead to aberrant β-catenin pathway activation. The dysregulation of this pathway in hepatic cancers makes it an attractive target for potential therapies, and experimental treatment in vivo has shown promising results. For example, inhibiting β-catenin expression by siRNA or R-Etodolac decreases proliferation and survival of human hepatoma cell lines.^15,16 Since cancer recapitulates development, determining the timing of β-catenin activation during hepatogenesis will help us to better understand the inappropriate activation of this pathway in hepatocarcinogenesis.Recent work has elucidated the role of β-catenin signaling in the liver, and has highlighted its essential role in liver health and disease.¹⁷ In addition, emerging evidence suggests that this pathway plays a key role in liver organogenesis.     

Risk assessment of transgenic apomictic tetraploid bahiagrass,cytogenetics, breeding behavior and performance of intra-specific hybrids

Pollen-mediated gene transfer from stress tolerant or herbicide-resistant transgenic plants may cause environmental or agronomic problems. Apomictic seed production found in some bahiagrass cultivars may serve as a natural transgene containment system. Under greenhouse conditions, the average gene transfer frequency from an herbicide-resistant apomictic tetraploid to a population of sexual diploid bahiagrass genotypes or apomictic tetraploid bahiagrass was 0.16% when the transgenic pollen donor was placed at 0.5–1.5 m distance from the non-transgenic pollen receptors. The herbicide-resistant hybrids were characterized for transgene integration, expression and ploidy, by Southern blot analysis, immuno-chromatography and flow cytometry, respectively. Hybrids resulting from open pollination of non-transgenic diploid female plants with transgenic tetraploid male plants were triploids or near-triploids, with 2n = 26–34. These hybrids displayed a wide range of phenotypic variability, including some non-persistent or non-flowering dwarf-type hybrids with good vigor, or hybrids with vegetative growth similar to non-transgenic plants, but with significantly reduced seed set. Non-flowering aneu-triploids with good vigor/field performance will provide the highest level of transgene containment. Embryo sac analysis of pollinated spikelets confirmed a high proportion of aborted ovules. An apospory-linked RFLP marker was detected in 13 of the 15 near-triploid hybrids. All flowering aneuploid hybrids displayed significantly reduced seed set, and none of the sexual near-triploid hybrids produced any seeds. All tetraploid gene transfer events carried the apospory-linked RFLP marker, suggesting that despite the presence of the aposporus locus, a low degree of sexuality co-exists in apomictic tetraploid cultivars. Thus, tetraploid apomictic bahiagrass does not provide complete transgene containment, although intra-specific gene transfer is drastically reduced compared to sexually reproducing perennial grasses.     

Identification and Genetic Characterization of Phenol-Degrading Bacteria from Leaf Microbial Communities

Microbial communities on aerial plant leaves may contribute to the degradation of organic air pollutants such as phenol. Epiphytic bacteria capable of phenol degradation were isolated from the leaves of green ash trees grown at a site rich in airborne pollutants. Bacteria from these communities were subjected, in parallel, to serial enrichments with increasing concentrations of phenol and to direct plating followed by a colony autoradiography screen in the presence of radiolabeled phenol. Ten isolates capable of phenol mineralization were identified. Based on 16S rDNA sequence analysis, these isolates included members of the genera Acinetobacter, Alcaligenes, and Rhodococcus. The sequences of the genes encoding the large subunit of a multicomponent phenol hydroxylase (mPH) in these isolates indicated that the mPHs of the gram-negative isolates belonged to a single kinetic class, and that is one with a moderate affinity for phenol; this affinity was consistent with the predicted phenol levels in the phyllosphere. PCR amplification of genes for catechol 1,2-dioxygenase (C12O) and catechol 2,3-dioxygenase (C23O) in combination with a functional assay for C23O activity provided evidence that the gram-negative strains had the C12O−, but not the C23O−, phenol catabolic pathway. Similarly, the Rhodococcus isolates lacked C23O activity, although consensus primers to the C12O and C23O genes of Rhodococcus could not be identified. Collectively, these results demonstrate that these leaf surface communities contained several taxonomically distinct phenol-degrading bacteria that exhibited diversity in their mPH genes but little diversity in the catabolic pathways they employ for phenol degradation.     

Identification of ATP binding residues of a protein from its primary sequence

Background  

One of the major challenges in post-genomic era is to provide functional annotations for large number of proteins arising from genome sequencing projects. The function of many proteins depends on their interaction with small molecules or ligands. ATP is one such important ligand that plays critical role as a coenzyme in the functionality of many proteins. There is a need to develop method for identifying ATP interacting residues in a ATP binding proteins (ABPs), in order to understand mechanism of protein-ligands interaction.     

Dynamic nature of a wheat centromere with a functional gene

Centromeric regions of higher eukaryotes are comprised mainly of tandem and non-tandem repeat sequences with variable copy number, spacing, order and orientation; are heterochromatic in nature, and are believed to be devoid of actively transcribing genes. Here, we report an actively transcribing wheat homolog of HSP70 gene that maps in the functional wheat centromere, and copy number of which seems to change in response to centromeric breaks. The HSP70 gene physically maps on the short arm of chromosomes 1A and 1D of Chinese Spring (CS) and 1R of rye. Whereas, on chromosome 1B in both ‘CS’ and Pavon background, the gene maps in the functional centromere as evident from its presence in both cytologically confirmed true ditelosomic lines Dt1BS and Dt1BL. Sequence comparison of 11 ESTs showed three sequence patterns suggesting that all three homoeologous copies of the gene are expressing. The cDNA-single stranded conformation polymorphism analysis confirmed expression of the ‘CS’ 1B copy of the gene. Observed in two independently developed Dt1BL lines, the 1B copy number of the gene showed three to fivefold increase in response to chromosomal breaks around the centromere. Putative gene duplications seem to involve large chromosomal segments as only one of the ten restriction enzymes used for DNA gel-blot analysis showed unique extra fragment band in the Dt1BL line. Further investigations are warranted to uncover the nature and mechanism of these duplications.     

Development of Transformation System of Verticillium lecanii (Lecanicillium spp.) (Deuteromycotina: Hyphomycetes) Based on Nitrate Reductase Gene of Aspergillus nidulans

A heterologous transformation system was developed for V. lecanii based on the complementation of a nitrate reductase mutant. Nitrate reductase mutants were obtained by resistance to chlorate in a rate of 23.24% when compared to other mutations that lead to the chlorate resistance. Mutant no. 01 and 04 was chosen for the transformation experiments. Plasmid pBT was used as transformation vector containing the Aspergillus nidulans nitrate reductase gene. A frequency of approximately 3 transformants/μg DNA was obtained using the circular vector pBT. The establishment of a transformation system for V. lecanii is fundamental for genetic manipulation of this microorganism.     

Effects of harvest residue and tillage on lesser cornstalk borer (Lepidoptera: Pyralidae) damage to sugarcane

Lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Cultural controls for E. lignosellus were evaluated in preparation for the potential loss of effective insecticides. Field studies conducted in 2006 compared the effects of harvest residues from green-harvested sugarcane (no preharvest burning to remove leaf matter) on E. lignosellus stalk damage and yield. Damage by E. lignosellus was significantly lower in plant cane plots that were covered with harvest residues collected from a green-harvested field before shoot emergence compared with plots without harvest residue. There were no yield differences between plots with and without harvest residues in plant or ratoon sugarcane fields in the 2006 study. The effects of three postharvest tillage levels (conventional, intermediate, and no tillage) were evaluated in preharvest burned and green-harvested fields in 2008 and 2009. Significantly less E. lignosellus damage was observed in the green- versus preharvest burned fields in both years. Intermediate and no-tillage plots had very little damage in green-harvested field. Conventional tillage plots had the greatest damage in the green-harvested field and the lowest damage in the preharvest burned field. In 2008, biomass yield was greater in the intermediate than conventional tillage in the green-harvested field, but it was greater in the conventional than in other tillage levels in the preharvest burned field. These studies demonstrated that cultural controls could greatly reduce E. lignosellus damage in sugarcane without the use of insecticides.     

Ontogenic Development of Corticotrophs in Fetal Buffalo (Bubalus Bubalis) Pituitary Gland

To evaluate the subpopulation of corticotrophs in developing buffalo (Bubalus bubalis) fetus, pituitary glands were recovered (n=6 per group) from late first, second and third gestational female buffalo dams. The corticotrophs were identified by using specific antibodies against proopiomelanocortin (POMC) and adrenocorticotrophic hormone (ACTH) through immunohistochemistry. There was a significant (P≤0.05) increase of immunoreactive (ir) ir-ACTH cells during late 2^nd trimester while, ir-POMC cells were more (P≤0.05) at late 3^rd trimester of gestation as compared to other age groups. The quantity of co-localized cells for POMC and ACTH was significantly (P≤0.05) greater at the end of 1^st gestation rather than 2^nd and 3^rd gestational fetal adenohypophyseal cells. This study is the first to demonstrate co-localization of POMC+ACTH and the affect of gestational age on the expression of these cells in buffalo fetus adenohypophysis.Key words: buffalo, corticotrophs, fetus, pituitary gland, immunohistochemistry     

Apolipoprotein A-V, triglycerides and risk of coronary artery disease: the prospective Epic-Norfolk Population Study

In mouse models, apolipoprotein A-V (apoA-V) exhibits triglyceride (TG)-lowering effects. We investigated the apoA-V/TG relationship and the association of apoA-V with coronary artery disease (CAD) risk by determining serum apoA-V levels and genotypes in a nested case-control (n = 1,034/2,031) study. Both univariate and multivariate apoA-V levels showed no association with future CAD (P = 0.4 and 0.5, respectively). Unexpectedly, there was a significant positive correlation between serum apoA-V and TG in men and women (r = 0.36 and 0.28, respectively, P < 0.001 each) but a negative correlation between apoA-V and LPL mass (r = -0.14 and -0.12 for men and women respectively, P < 0.001 each). The frequency of the c.56C>G polymorphism did not differ between cases and controls despite significant positive association of c.56G with both apoA-V and TG levels. For -1131T>C, the minor allele was significantly associated with lower apoA-V yet higher TG levels and was overrepresented in cases (P = 0.047). The association of -1131T>C with CAD risk, however, was independent of apoA-V levels and likely acts through linkage disequilibrium with APOC3 variants. The positive correlation of apoA-V levels with TG levels, negative correlation with LPL levels, and lack of association with CAD risk highlight the need for further human studies to clarify the role of apoA-V.